1. Field of the Invention
This invention relates to the field of fire alarm strobe light control systems and other strobe light systems, particularly to systems which allow for disparate strobe triggered devices to provide light pulses simultaneously.
2. Description of the Related Art
Epilepsy is a common chronic neurological disorder characterized by recurrent unprovoked seizures that affects more than three million Americans. For about three (3) percent of them (approximately two per 10,000 of the general population), exposure to flashing lights at certain intensities or in certain visual patterns can trigger seizures. This condition is known as photosensitive epilepsy and is most common in children and adolescents.
The visual triggers for photosensitive epileptic seizures are generally cyclic visual cues that form a regular pattern in time and space. Flashing lights, commonly known as “strobes” or “strobe lights,” are examples of patterns in time that can trigger photosensitive epileptic seizures and, in fact, these are the most common triggers.
While strobes can have a negative adverse affect on those individuals susceptible to photosensitive epileptic seizures, they are also are beneficial to the general population in a wide variety of scientific, industrial and commercial applications. For example, strobe lights are used in the entertainment industry, such as in clubs and in video games, to give an illusion of slow motion (i.e., the stroboscopic effect). Other applications for strobe lights are in the public safety field due to the inherent ability of flashing lights to attract visual attention. For example, strobe lights are used in alarm systems, in law enforcement and other emergency vehicles, and even in aircraft anti-collision lighting, among other applications. In fact, use of strobe lighting in fire alarm systems is mandated by the American Disabilities Act (the “ADA”), which states that workplaces and places serving the public are required to have fire alarms which flash as well as ring so that individuals who can not hear or have impaired hearing function are alerted to the emergency situation.
While strobe lighting used in the aforementioned entertainment applications can be avoided by those subject to potential photosensitive epileptic seizures, strobe lighting used in public safety applications is not as easily avoided. In recognition of the potential of strobes utilized in these emergency and public safety applications to initiate seizures, the ADA mandates that fire alarm strobe signaling devices be synchronized to inhibit the triggering of seizures in individuals suffering from photosensitive epilepsy. By providing synchronization and specific strobe timing, the potentially dangerous interaction between different flashing devices used in alarm systems is virtually eliminated and, so long as specific flash patterns are utilized, the triggering of photosensitive epileptic seizures is generally inhibited.
The UL 1971 standard, “Signaling Devices for the Hearing Impaired,” is generally the synchronization and timing standard for visual notification devices utilized by those involved in the industry to provide safer strobe warning devices and systems. Specifically, this standard requires that all visible signaling devices triggered by the same event flash within a 0.01 second time frame and maintain a one- to two-hertz flash rate (one to two flashes per second).
In order to ensure compliance with the UL 1971 industry standard and the mandates of the ADA, manufacturers of the visual notification aspects of alarm and public safety systems define a specific method of powering and controlling individual strobe lights within the system as a whole such that each strobe flashes in-sync within the confines of the UL 1971 standard (i.e., within a 0.01 second time frame and at the specified cyclic rate). This method of synchronization, and the process and signal utilized to implement it, is typically referred to as a “Synchronization Protocol” within the industry. For example, in a fire alarm system, the synchronization protocol signal is generally generated by a synchronization supply expander designed for use with that manufacturer's strobes, or a fire alarm control panel similarly designed for use with the strobe system.
Several different companies manufacture strobe signaling devices for fire alarm applications and each traditionally has utilized a unique synchronization protocol to control and synchronize the operation of its strobe signaling devices. While these strobe signaling devices provide companies with assurance that their unique synchronization protocol will work with their own manufactured strobe signaling devices, it has left the consumer with a lack of commercial options. For example, since the synchronization protocol is specific to the company's strobe signaling products and fire alarm applications, generally a particular companies synchronization protocol can only be utilized with that company's strobe and fire alarm products. This means that the end consumer is often shoe-stringed into the types of devices they can use—i.e., they can only use those devices sold by the manufacturer of the synchronizing protocol system. This forced collective purchase robs the consumer the bargaining power of competition and choice in the marketplace; they cannot shop for the best price and value for each component of the alarm system (i.e., buying the individual strobes and synchronization protocol from different manufacturers).
For example, the current status of synchronizing protocol systems in the industry generally function as follows. As indicated above, the flash/strobe characteristics of alarm and visual notification devices utilized in emergency applications are generally controlled via a synchronization protocol. Generally, this protocol is generated by interrupting the power source to the strobe devices with brief synchronization pulses (a.k.a. “sync pulses”). These sync pulses are imposed by the power supplying device (e.g., a synchronization module, fire alarm powder expander or firm alarm control panel), and are detected by the visual notification device. By means of these pulses, the timing of the strobe flash of each individual light can be controlled.
Generally, to maintain the UL 1971 requirement that the flash rate be between one- to two-hertz, the pulses are issued at a one second nominal rate. As show in FIG. 1 however, the relationship between the sync pulse and the timing of the resultant strobe flash can be different depending on the design and operation of the different manufacturer's systems. This timing discrepancy between manufacturers is exemplified in FIG. 1. As shown, the period of time after the start of the receipt of the sync pulse until the strobe flash begins is different between the systems of Manufacturer A and Manufacturer B. For Manufacturer C, the difference is even more pronounced as this manufacturer uses the tail, instead of the start, of the sync pulse to synchronize the resultant flashes. Thus, each manufacturer uses a different time period of the strobe flash of its strobe flashing devices to time and synchronize the system.
Historically, therefore, the only method of meeting UL 1971 requirements was to use strobe (and control) devices from only one manufacturer in a given installation—the individual strobe lights and the synchronization protocol used to sync them must be from the same manufacturer as otherwise the disparate timing of different manufacturers would result in the single timing signal producing out of sync flashes, as the separate strobe lights would flash out of sync with each other. This restriction limits flexibility in both new system installation, where a consumer generally has to select a single manufacturer's products, and in retrofit applications. Further, it inherently requires the time and cost associated with 1) ascertaining the manufacture of the strobe; and 2) figuring out the particular synchronization protocol utilized by the manufacturer of said devices. Retrofit applications can be particularly problematic because in such a situation the original manufacturer may no longer exist or may no longer use the same synchronization methodology. In this situation, a retrofit may require replacement of completely functional devices simply because they cannot be used in conjunction with new components. Thus, both the cost and time associated with the installation and/or retrofit/restoration of sync-ed strobe light public safety alarm systems is needlessly augmented.